The present invention relates to a fail-safe system for an automatic car driving system wherein a throttle valve is automatically controlled, and more particularly to a system for preventing troubles caused by failures in the automatic driving system.
In an example of the automatic driving system, a plurality of cameras are mounted on the vehicle to monitor forward conditions such as a behavior of a front-running vehicle (a vehicle which is running in front). A control unit processes image data picked up by the camera to determine acceleration and deceleration of the front-running vehicle, and drives a motor to operate a main throttle valve of the present vehicle dependent on the acceleration and deceleration of the front-running vehicle. An auxiliary throttle valve is further provided adjacent the main throttle valve to control traction of the vehicle.
In such a tandem throttle device, the auxiliary throttle valve is widely open when the vehicle is driven without slipping. If the motor for operating the main throttle valve or a throttle position sensor fails during the automatic driving, the main throttle valve may be maintained to be opened at a large degree. With the both valves widely open, the vehicle speed undesirably increases. Thus it is necessary to provide a fail-safe system which renders the automatic driving system inoperative when a device thereof fails. It is further necessary to allow the engine to be properly operated through other auxiliary means when the automatic driving system does not work.
Japanese Patent Application Laid-Open 2-271034 discloses a fail-safe system for the tandem throttle device. The main throttle valve is electronically controlled by a motor and the auxiliary throttle valve is operated in accordance with the operation of an accelerator pedal. When the motor for the main throttle valve fails, the auxiliary throttle valve is operated to control the power of the engine. However, the fail-safe system is not for the automatic driving system. Moreover, the system cannot detect the failure of devices such as the motor and a throttle position sensor, and errors caused by displacement of the sensor from a set position.
Japanese Patent Application Laid-Open 63-314330 discloses a fail-safe system having an auxiliary throttle valve urged in the closing direction by a spring which is operated by a solenoid. When the main throttle valve fails, the auxiliary valve is closed by the spring. Neither of the conventional system is a fail-safe system for the automatic driving system. Since the auxiliary valve is closed at the failure, the driver cannot drive the vehicle by operating the accelerator pedal.